Dual-fuel internal combustion engines are typically operated in several operating modes. In this case, we differentiate an operating mode with a primary liquid fuel supply (“liquid operation” for short; in the case of the use of diesel as a liquid fuel, it is called “diesel operation”) and an operating mode with primarily gaseous fuel supply, in which the liquid fuel serves as a pilot fuel for initiating combustion (called “gas operation” or also “pilot operation” or “ignition jet operation”). An example of the liquid fuel is diesel. It could also be heavy oil or another self-igniting fuel. An example of the gaseous fuel is natural gas. Other gaseous fuels such as biogas, etc. are also suitable.
In pilot operation, a small amount of liquid fuel is introduced into a piston cylinder unit as a so-called pilot injection. As a result of the conditions prevailing at the time of injection, the introduced liquid fuel ignites and detonates a mixture of gaseous fuel and air present in a combustion chamber of the piston cylinder unit. The amount of liquid fuel in a pilot injection is typically 0.5-5% of the total amount of energy supplied to the piston cylinder unit in a work cycle of the internal combustion engine.
The substitution rate indicates the proportion of the energy supplied to the internal combustion engine in the form of the gaseous fuel. Substitution rates of between 95 and 99.5% are targeted.
In addition, there is still a mixed operation, in which substitution rates of less than 95% are used.
Moreover, it is known that the internal combustion engine or control unit can be operated in a changeover mode, which is used to switch between the different operating modes during operation. In principle, in the changeover mode, an amount of energy supplied to at least two combustion chambers through the gas-air mixture is changed in a first direction, and an amount of liquid fuel supplied to the at least two combustion chambers is changed in an opposite second direction.
U.S. Pat. No. 7,913,673 A1 discloses a dual-fuel internal combustion engine. A disadvantage of the dual-fuel internal combustion engine of this reference is that an undesirable deviation of the rotational speed or the torque up to the so-called overfueling can occur during a changeover phase, for example from liquid operation to pilot operation. In a critical case, too much energy is supplied to the internal combustion engine.
Internal combustion engines of this type may have a central gas mixer for the at least two combustion chambers. The distance of the at least two combustion chambers from the at least one gas mixer results in a transport delay of the gas-air mixture. The disadvantage of this is that the internal combustion engine can therefore behave unpredictably in the changeover phase.